1. What an off-grid solar system is
An off-grid (or «island») system produces and uses its own energy without exchanging it with the grid: what the panels produce goes to the house or into the battery, and nothing is fed into the grid. With the CEG Growatt you can also keep the grid as a backup: the system works as an island and the grid only comes in when needed, through an ATS, contactors or a changeover switch.
Check the period with the worst balance between generation and demand for your location and use. The yearly average alone cannot show autonomy.
2. The components
Panels and strings: follow the model’s PV power, cold voltage, current and MPPT limits. SPF 6000 ES Plus has two MPPTs; total power alone does not give a universal limit per string. String calculator
- CEG string box: string fuses, surge protectors, isolator switch. DC string box
- Growatt SPF 6000 ES Plus CEG inverter: solar charge controller, battery charger and inverter in one unit. Growatt inverter
- CEG 51.2 V battery LiFePO4, with BMS and battery circuit breaker built in. Batteries
- AC protections: circuit breakers, RCD, surge protectors. Materials
- Switching (if there is a grid or a generator): ATS, interlocked contactors or manual 1-0-2 changeover switch. CEG diagrams
3. How it connects
The block diagrams are on the CEG Diagrams page (CEG diagrams). For the detailed wiring diagram, ask Carmine.
4. Sizing in 4 steps
- Daily use in kWh: use measured consumption or the energy label. For a fridge, divide kWh/year by 365. This is an average, not compressor power multiplied by 24 hours. Current washing-machine labels show kWh per 100 Eco 40–60 cycles: divide by 100 and multiply by your washes. Seasonal figures for heat pumps and air conditioners use test conditions; adjust them to your climate and use. For a constant load, W × hours ÷ 1,000 = kWh. Battery calculator
- Autonomy: choose the days without sun to cover, taking grid or generator backup into account.
- Battery: nominal capacity ≈ daily use × days ÷ (usable share × efficiency). Example: 0.90 usable share and 0.95 efficiency. Actual values depend on the system. Also consider temperature, ageing and available power.
- Panels: check the period with the worst balance between generation and demand for your location and use. A first estimate is daily use ÷ (peak sun hours × total efficiency). Count losses only once. Solar planning tool
Choose the inverter for loads used together and start-up peaks. For strings, use panel open-circuit voltage and its temperature coefficient at the local minimum temperature. Also check currents and the MPPT range. Inverter calculator · String calculator · Autonomy calculator
5. Cables
- One 6 kW Growatt: Carmine suggests at least 35 mm² for each positive and negative cable, with up to 1.5 m between battery and inverter. Ask Carmine.
- One 12 kW Growatt SPE 12000 ES: two positive and two negative cables, each at least 35 mm², up to 1.5 m, in the CEG setup with two batteries in parallel. The manual lists 2 × 2 AWG (about 33.6 mm² per conductor). Ask Carmine.
- Two SPE 12000 ES units in parallel: four positive and four negative cables, eight conductors in total. Each inverter keeps its own battery connections. Ask Carmine.
- Over 1.5 m: Carmine suggests 50 mm² per conductor. This does not cover every length. The installer must check current capacity, voltage drop, terminals and protection for each branch. Parallel conductors need matching lengths and properties and correct current sharing.
- AC side: CEG diagrams use 6 mm² for 6 kW and 10 mm² for 12 kW, with 32 A and 63 A output breakers respectively. Check these references for installation method, temperature, length and protection coordination. Ask Carmine.
- Earth: in the CEG diagram the system earth cable has the same cross-section as phase and neutral: 6 mm² on the 6 kW, 10 mm² on the 12 kW. The cable from the equipotential bar to the house earth electrode is usually 16 mm² and is chosen by the electrician. These are CEG diagram values: the electrician checks them on the real installation. Ask Carmine.
Use the cable calculator for an initial estimate, then have the installer check it. Cable calculator
In the CEG diagram with a 6 kW single-phase grid supply, Carmine suggests one shared 32 A input breaker, including when several inverters work in parallel. This applies to that setup. Your electrician must check the supply line, bypass operation, battery charging and the manufacturer’s requirements. Ask Carmine about the CEG diagram.
6. Generator
The GEN input and dry contact can manage an auto-start generator if the generator and its interface are compatible. The dry contact is a control signal, not a power supply for the starter motor. Thresholds, power, supply quality and charging current must follow the manuals. The CEG diagram uses a 1-0-2 switch for an alternative emergency supply. Ask Carmine and your electrician about settings and wiring. CEG diagrams
7. Neutral and earth
On the CEG Growatt units he tested, Carmine reports readings of about 0 V between output neutral and the case. This is a test observation. It does not replace the manufacturer’s internal diagram or prove how the unit behaves in every mode, including bypass.
In the video, Carmine describes tests on some inverters with a floating output. Earthing the output depends on the model. Before any work, the electrician must check the manufacturer’s manual and test the protective devices. These tests are not a wiring plan for other inverters. N marks the terminal named neutral by the manufacturer; this alone does not authorise an earth connection. Ask Carmine or your electrician about your model. Video
8. Rules and paperwork in Italy
In Italy, electrical work serving buildings must be done by an authorised company under D.M. 37/2008, with a declaration of conformity and its attachments. A qualified professional designs the system when required; the company’s technical manager does so in the other cases allowed. The company checks filing duties. Building permits, site restrictions, tax duties and incentives depend on the case: check with the authorities and a tax adviser before work. No export to the grid does not remove all duties. For batteries and rooms, follow environmental protection, temperature, clearance and manufacturer requirements. Outdoor use is allowed only for suitable products. Use the proper collection route at end of life. CEI 64-8 and off-grid
9. Examples
- Home, 6 kWh/day and 1.5 days of autonomy: with a 90% usable share and 95% efficiency, estimated nominal capacity is 6 × 1.5 ÷ (0.90 × 0.95) ≈ 10.5 kWh. This is an example, not a guaranteed capacity. Use local and panel data for PV and strings. Solar planning tool
- Weekend cabin: consider use days, consumption, charging between visits and a compatible backup generator.
- Existing grid-tied solar: check Magic Box compatibility and layout before buying. Magic Box
10. Carmine's videos (in Italian)
11. FAQ
Is an off-grid system legal in Italy?
Yes, if the system is built properly: electrical work must be done by a qualified company (D.M. 37/2008), which issues the declaration of conformity, in line with the CEI 64-8 standard. Permits and restrictions depend on the case: check with the competent authorities. For your system, ask Carmine.
Can I keep the grid as a backup?
Yes, with correctly designed switching that prevents accidental parallel operation with the grid.
How many days of autonomy do I need?
Check the period with the worst balance between generation and demand for your location and use. The yearly average alone cannot show autonomy.
Lithium or lead-acid battery?
CEG LiFePO4 batteries do not need topping up. Follow the manufacturer’s instructions for periodic checks. Ask Carmine about any doubts or faults.
Are tax incentives available?
For off-grid it is not clear: ask Carmine for information and details. Tax requirements must still be checked with a qualified adviser.
Can I install it myself?
In Italy, electrical work serving buildings must be done by an authorised company under D.M. 37/2008, with a declaration of conformity and its attachments. A qualified professional designs the system when required; the company’s technical manager does so in the other cases allowed. The company checks filing duties. Building permits, site restrictions, tax duties and incentives depend on the case: check with the authorities and a tax adviser before work. No export to the grid does not remove all duties. For batteries and rooms, follow environmental protection, temperature, clearance and manufacturer requirements. Outdoor use is allowed only for suitable products. Use the proper collection route at end of life.
How do I see the system on my phone?
With a compatible data logger and ShinePhone, you can view the data available from your system. Battery and SOC readings depend on the BMS, communication and settings. Ask Carmine about registration, any installer code needed and connection of products bought through CEG.